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        //1.绝对值
        console.log(Math.abs(-1));
        console.log(Math.abs('-1'));//隐式转换  会把字符串型  -1  转为数字型
        //2.三个取整方法
        //(1) Math.floor()   向下取整  往最小取值
        console.log(Math.floor(1.1));//1
        console.log(Math.floor(1.9));//1
        //(2) Math.ceil()    向上取整  往最大取值
        console.log(Math.floor(1.1));//2
        console.log(Math.floor(1.9));//2
        //(3) Math.round()   四舍五入  其他数字都是四舍五入，但是  .5  特殊 它往大取值
        console.log(Math.round(1.1));//1
        console.log(Math.round(1.9));//2
        console.log(Math.roynd(-1.5));//-1
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